JEE MAIN - Chemistry (2002 - No. 40)
If half-life of a substance is 5 yrs, then the total amount of substance left after 15 years, when initial amount is 64 grams is
16 grams
2 grams
32 grams
8 grams
Explication
$${t_{1/2}} = 5\,\,$$ years, $$T=15$$ years hence -
total number of half life periods $$ = {{15} \over 3} = 3.$$
$$\therefore$$ Amount left $$ = {{64} \over {{{\left( 2 \right)}^3}}} = 8g$$
total number of half life periods $$ = {{15} \over 3} = 3.$$
$$\therefore$$ Amount left $$ = {{64} \over {{{\left( 2 \right)}^3}}} = 8g$$